1. Field of the Invention
The present invention relates to a machining apparatus and a machining method for machining a workpiece by rotating a tool and the workpiece relatively and, more particularly, to an apparatus and a method for rotating and revolving either the tool or the workpiece.
2. Related Art
A machining operation such as a cutting or grinding operation is generally performed by rotating a tool and a workpiece relative to each other. For example, a boring operation or cutting operation is performed by running the tool along a cylindrical surface of the workpiece to cut an inner face of the cylindrical surface continuously; similarly, an end milling operation for cutting an inner face of a cylindrical surface is performed by rotating a tool having cutting blades on its outer circumference to cut the inner face of the cylindrical surface and by moving the tool in the circumferential direction along the cylindrical surface so as to change portions to be cut.
In the former boring operation, a cutting blade runs along the surface to be cut, so that the cutting operation is continuously performed to enhance the amount of cutting per unit time, i.e., the working efficiency, and a cut surface (or cut portion) is continuously formed to improve the roughness of a worked surface. Since the cutting blade is exposed to the cutting load at all times and is seriously heated to a high temperature, on the contrary, the cutting speed or the working efficiency is restricted by the life of the cutting blade. In other words, if the cutting conditions are set by considering the working efficiency preferentially, the tool is so seriously worn as to cause a problem that the cost of tools rises to raise the cost of the working operation.
In the latter end milling operation, on the other hand, an end mill is moved, while being rotated on its axis, in the circumferential direction of the cylindrical surface, so that its cutting operation is intermittently performed. The cutting blades are exposed to an impact load, but their edges are air-cooled, so that the temperature conditions for the cutting blade are moderated. On the contrary, the speed to move the end mill in the circumferential direction of the cylindrical surface is mechanically restricted so that the cutting speed cannot be especially raised to a high level. This invites a problem that the working efficiency is lowered although the cutting width can be enlarged and another problem that the intermittent cutting operation deteriorates the roughness of the worked surface. In order to improve the roughness of the worked surface, the circumferential moving speed of the end mill on the cylindrical surface may be lowered. Then, there arises a disadvantage that the working efficiency is further lowered.
In Japanese Patent Laid-Open No. 63-34010 (JP-A-63-34010), there is disclosed one example of the tool for performing the end milling operation having the aforementioned characteristics. The disclosed end mill is a roughing end mill, in which a helical groove and a helical cutting portion defined by this groove are formed in a stem portion of its body and in which undulating edges are formed in the cutting portion to have undulations shifted by a predetermined phase for each edge.
The roughing end mill of the prior art, as disclosed in the aforementioned Laid-Open, is constructed to transfer the waveforms of the cutting edges to the surface to be worked. The end mill performs the cutting operation by rotating on its center axis, as in ordinary end mills of prior arts, while revolving around the center of the surface to be worked, so as to change the portions to be cut. In this case, like the prior arts, the rotational speed is far higher than the moving speed of the end mill along the worked surface so that the cutting speed is substantially determined by the rotational speed of the end mill. This makes it difficult to improve the durability of the cutting blade and the working efficiency or the roughness of the worked surface at the same time.